The present invention relates generally to microwave excited ultraviolet lamp systems and, more particularly, to a reflector for use in such lamp systems to reflect ultraviolet radiation generated by a plasma lamp bulb mounted within the system.
Ultraviolet lamp systems are designed for coupling microwave energy to an electrodeless lamp, such as an ultraviolet (UV) plasma lamp bulb mounted within a microwave chamber of the lamp system. In ultraviolet lamp heating and curing applications, one or more magnetrons are typically provided in the lamp system to couple microwave radiation to the plasma lamp bulb within the microwave chamber. The magnetrons are coupled to the microwave chamber through waveguides that include output ports connected to an upper end of the chamber. When the plasma lamp bulb is sufficiently excited by the microwave energy, it emits ultraviolet radiation through a bottom end of the microwave chamber. UV lamp systems used in curing of adhesives, sealants or coatings, for example, include a reflector mounted within or that form a part of the microwave chamber in which the plasma lamp bulb is positioned. The reflector may be made of coated glass or metallic, and is operable to focus the emitted ultraviolet radiation in a predetermined pattern toward the substrate to be irradiated. Typically, the ultraviolet lamp system includes a mesh screen mounted to the bottom end of the chamber that is transmissive to ultraviolet radiation but is opaque to the microwaves generated by the magnetrons. It will be appreciated that the terms xe2x80x9cupper endxe2x80x9d and xe2x80x9cbottom endxe2x80x9d are used herein to simplify description of the microwave chamber in connection with the orientation of the chamber as shown in the figures. Of course, the orientation of the microwave chamber may change depending on the particular ultraviolet lamp heating or curing application without altering the structure or function of the microwave chamber in any way.
In UV lamp systems, the plasma lamp bulb is cooled by pressurized air that is supplied by a pressurized air source associated with the lamp system. In most lamp system designs, the pressurized air must pass through the reflector to the region of the microwave cavity in which the plasma lamp bulb is mounted. In those designs that use a metallic reflector that also forms part of the microwave chamber, the reflector may include one or more longitudinally extending rows of apertures formed through the reflector that are operable to pass air toward the plasma lamp bulb. The longitudinally extending rows of apertures are typically aligned generally parallel with the longitudinal axis of the plasma lamp bulb, and the apertures may have many different shapes and sizes.
Alternatively, when the reflector is made of coated glass in which it is generally too costly to form apertures through the glass, the reflector is typically constructed as two reflector panels with a single longitudinally extending slot formed between the reflector panels that is generally aligned with the longitudinal axis of the plasma lamp bulb. With this reflector configuration, the slot is operable to pass air toward the plasma lamp bulb so that the air splits about opposite longitudinal sides of the bulb to cool the bulb. However, this reflector configuration has the drawback that the air does not envelop the bulb effectively entirely about its outer surface, so regions of the bulb, particularly the region on the underside of the bulb remote from the slot, are not sufficiently cooled by the air. As a result, the operating life of the plasma lamp bulb may be diminished and/or the volume of air passed through the slot must be increased to achieve sufficient cooling of the bulb.
Thus, there is a need for a reflector that is configured to efficiently pass air toward a plasma lamp bulb in a microwave excited ultraviolet lamp system to cool the bulb. There is also a need for a reflector configuration that reduces the amount of cooling air required to operate the plasma lamp bulb at a predetermined power level. There is also a need for a reflector configuration that improves the operating life of the plasma lamp bulb.
The present invention overcomes the foregoing and other shortcomings and drawbacks of reflectors heretofore known in microwave excited ultraviolet lamp systems. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
According to one aspect of the present invention, the reflector includes a pair of reflector panels that are mounted in opposing, i.e., mirror facing relationship within the microwave chamber, and in spaced relationship to the plasma lamp bulb. A longitudinally extending intermediate member is mounted in spaced relationship to the pair of reflector panels and to the plasma lamp bulb. The pair of reflector panels and the intermediate member form in mounted combination a pair of longitudinally extending slots that are operable to pass air toward the plasma lamp bulb. The pair of slots are positioned relative to the plasma lamp bulb so that the air envelops the plasma lamp bulb effectively entirely about its outer surface. The pair of slots are oriented so that the air passes along opposite longitudinal sides of the plasma lamp bulb and then merges generally in a region beneath the bulb that is remote form the pair of slots.
In accordance with one aspect of the present invention, the pair of longitudinally extending slots may be aligned generally parallel to and offset from the longitudinal axis of the plasma lamp bulb. Alternatively, each of the longitudinally extending slots may have a sinusoidal or other configuration that is also operable to pass the air toward the bulb so that the air envelops the bulb effectively entirely about is outer surface to cool the bulb.
In accordance with another aspect of the present invention, a reflector is provided that includes a pair of reflector panels that are mounted in opposing relationship, and that are connected to opposite longitudinal edges of the intermediate member. In this reflector configuration, the intermediate member includes multiple apertures formed therethrough that are operable to pass air toward the plasma lamp bulb to envelop the bulb effectively entirely about its outer surface. The apertures may be provided in two longitudinally extending rows that are generally parallel to and offset from the longitudinal axis of the plasma lamp bulb. The apertures of one row may be staggered relative to the apertures of the other row.